Researchers report progress in ensuring that postmenopausal women can still have enjoyable sex lives.

Two new studies report benefits from two potential treatments that may help increase sexual drive for women who either have gone through menopause or have had a hysterectomy.

Sexual desire often declines during menopause. During this time, which usually occurs around age 51 in the U.S., a woman’s ovaries stop producing the sex hormones estrogen and progesterone. Women also stop getting their menstrual periods and can no longer get pregnant naturally.

Menopause can bring about many changes for a woman. The vaginal and genital tissue may get thinner, which can cause painful sex, or dyspareunia. Almost 40 percent of women will experience dyspareunia in their lifetime, especially during menopause, according to Dr. Lynne T. Schuster, a physician at Mayo Clinic's Women's Health Clinic in Rochester, Minn. Women may also suffer from vaginal dryness and loss of elasticity during this time.

The first of the new studies looked at how the male sex hormone testosterone may be able to help increase libido in women who have had a hysterectomy. The women were between the ages of 21 and 60 and had lower than average levels of testosterone. They were all taking estrogen, and were either given a placebo or different doses of testosterone enanthate -- a common injectable form of the hormone -- for six months.

Testosterone has not been approved as a treatment for women by the Food and Drug Administration. Women who undergo menopause naturally usually still produce the male hormones, but those who have their ovaries removed through a hysterectomy have a sharp drop in testosterone levels.

Women who received the highest dose of testosterone -- 25 milligrams weekly -- had significant boosts in their sexual desire and other measures of sexual function. They had nearly three more sexual encounters per week after the treatment compared to before the study. They also had greater lean body mass and muscle strength.

The groups taking the lower doses of testosterone or placebo did not experience significant changes in libido.

It is important to note that taking 25 milligrams weekly boosted the subject’s testosterone levels to five or six times what's considered a healthy level. However, the researchers said there were no serious negative side effects they found. High doses of testosterone previously have been linked to negative heart effects including drops in "good" HDL cholesterol levels, but the researchers found the women’s total and LDL cholesterol, triglycerides, and fasting glucose did not change notably. There was a slight decrease in HDL, but that could have been due to chance.

The other study looked at a non-hormonal treatment called flibanserin, which had previously been submitted to the FDA for approval. It was not given the OK at that time because the agency felt the benefits were not that much greater than those seen in placebo-takers. The treatment has been resubmitted for approval since.

This new study looked at 949 postmenopausal women with very low sexual drives. A little less than half of them were given 100 milligrams a day of flibanserin for six months.

Those taking flibanserin reported increases in the number of satisfying sexual encounters and a higher score on a sexual desire scale compared to those on placebo. About 38 percent of women on flibanserin said they experienced benefits to their sex lives after they took the treatment, compared to only 20 percent of the women on the placebo.

Thirty percent of the women on the treatment experienced side effects including dizziness, sleepiness, nausea, and headaches, but ultimately only 8 percent stopped the treatment because of them.

Both studies were published Dec. 4 in Menopause, the journal of the North American Menopause Society.

Another option for women experiencing these issues is low-dose vaginal estrogen treatments to help treat these issues. Low-dose vaginal estrogen treatments have been found to be generally safe for women who do not have a history of breast cancer or special risk factors for the disease.

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